With no other nodes in the graph, attributes are implicitly passed through, so input P goes to output P, input N to output N etc ie, the geometry is unchanged. The rightmost node represents the final output of a point. The leftmost node represents a single point, and all its standard built-in attributes position, colour, normal, id etc. Anything you do in this graph is run on all the points of your geometry simultaneously, or at least as simultaneously as your computer will allow. In a vops network, the houdini chant that 'everything is points' becomes very important. They flow left to right rather than top to bottom. Here you find a new type of node graph, one that is also used for houdini shaders (SHOPS).
Hit enter, or double click, to go into its sub network. It helps to think of the vop network like a flowchart, reading left to right. I explain vops a little more in Houdini Vops, but you can think of vops as a way to make your own deformers, using nodes. 
Vops are node based programing, sort of like hypershade/the node editor in Maya, but way more powerful. Older tutorials use point sops, you're better off getting comfortable with vops or vex. List of renderman SL variables for comparison: Point Sopĭon't use point sops. List of recognised houdini attributes (the amount surprised me, I use maybe 10% of these): 'P' is position, 'N' is normal, and so on. Why 'Cd'? Houdini uses a lot of naming conventions derived from prman. I added a colour node to the grid to make it red, another to make the sphere green, so you can see what's going on. Eg, you want to transfer colour, normal, and pscale, you'd type "Cd N pscale". If you want more than one attribute transferred, separate them with a space. Same as before, just type 'Cd' in the list of transferred attributes. Houdini scene: File:attribute_transfer_color_and_position.hip
The 'match P attribute' is required because usually people don't want this they'll be transferring colour, or some other attribute, but they don't want the points to actually move. Yes houdini has regular poly and nurbs spheres too, look in the 'primitive type' dropdown of the sphere SOP. In maya-speak, we're reading a single particle (that we visualise as a sphere), read its position, compare to each vertex in a grid, and warp those verts towards the particle if they're too close. Knowing that, this setup makes a little more sense. It's more like a single maya particle rendered in sphere mode ie it has position and scale, but no verts that make up the surface. The answers are that a default houdini sphere (called a primitive sphere) isn't like a maya nurbs or poly sphere. 'But hang on, you said we're basically manipulating verticies, how come this setup magically reads the transform of the sphere? And shouldn't the grid verts be warping to all the verts on the sphere surface?' Good questions. 
(In fact you see this happen before you modify the distance and blend with parameters).
If you had no falloff, the entire grid would disappear to a single point at the center of the sphere.
This setup reads the position of the sphere, and transfers it to each point on the grid, with falloff. In houdini, all the fun stuff is down here, getting messy, pushing points around. While in maya you rarely modify these directly (usually you stay one level higher and manipulate object transforms). In maya you'd say this are the vertex positions. P is the standard attribute for position, usually point position. On second tab set the distance low (say 0.1) and blend width up (say 2.0) to get a blendy warp like the soup version.Ī few things to take note of here (or come back to later after you've tried a few more examples) :. Wire grid into first input, sphere into second. Transfer the position of sphere to the points of a grid, with a smooth falloff. Houdini scene: File:attribute_transfer_position.hip 56 Variable tricks with set and setenv and varchange. 53 Procedural growth via edge transport. 49 Transform packed prims with instance attributes. 46 Attribute Wrangle and iq colour ramp. 41 Chops to load audio and create animated waveforms. 36 Create edges with connect adjacent pieces sop. 34 Folding objects (the transformers cube effect). 29 For-each node to make greebles and city blocks. 28 Explicit rotation/orient control for copy and instances. 27 Ball of Eyeballs with Copy and Packed primitives. 25 Random Instance with Copy to Points and Piece Attribute. 24 Effector for scale, rotation, colour. 18 Attributes as groups, or groups with syntax. 13 Point and attribute transfer with lag via solver sop. 12 Point and attribute transfer together. 6 Hscript, Vops, Vex (and python), which to use?.
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